Conventionally, a high-Cr-containing Ni-based alloy that contains Cr near the solid solubility limit of Ni has been known as a heat-resistant alloy having high temperature corrosion resistance, and as a corrosion-resistant alloy having corrosion resistance, demonstrating very high performance in each of these aspects.
For example, such an alloy has been used to make a metal member for use in a waste gas environment of a boiler for thermal power generation in which fossil fuel, such as heavy oil and coal is burned, making use of an advantageous characteristic of high temperature corrosion resistance.
Furthermore, in order to improve power generation efficiency, such a boiler for thermal power generation in which fossil fuel, such as heavy oil and coal, is burned, has been improved to increase a vapor temperature inside a boiler tube. The boiler tube itself has a temperature lower than the ambient temperature because the boiler tube is externally reheated by a combustion waste gas, so that a metal member directly contacting with the boiler tube is cooled by the boiler tube, resulting in reduction in high temperature corrosion.
However, since a vapor temperature passing through the boiler tube is increasing, erosion caused by high temperature corrosion including sulfuration increases markedly. In such a situation, a 50Ni-50Cr alloy, which is known to have superior sulfuration resistance, has been employed to form a supporting member of the boiler tube.
However, the 50Ni-50Cr alloy has low workability, so that it cannot be subjected to hot forging and is provided as a cast product. However, because such a product is a cast, there are limitations on its shape, and cold workability in bending, for example, is also insufficient.
For example, an alloy having a composition near that of the 50Ni-50Cr alloy and developed in view of the demand for improved workability is a “corrosion-resistant Ni—Cr-based alloy having superior bend formability” disclosed in Patent Document 1.
This alloy can be subjected to hot forging and has superior cold workability, so that this alloy can be formed into a bent shape for controlling a waste gas flow pass.
However, although the “corrosion-resistant Ni—Cr-based alloy having superior bend formability” disclosed in Patent Document 1 barely enables hot forging of a cast, hot workability is poor, so that it is difficult to form into a shape such as a seamless pipe, which is required to be shaped at high temperature, and additional problems such as poor corrosion resistance of a welded portion occur.
Furthermore, Patent Document 2 proposes a 50Ni-50Cr alloy with hot workability improved by controlling alloy component contents, in particular, the content of Ca, Mg, B, rare earth elements, and Zr. However, mechanical properties, corrosion resistance and the like of this alloy are still not sufficient, and accordingly, fields of application in industrial use are limited.
Then, a “Ni-based alloy having superior high temperature workability and having superior corrosion resistance with a significantly small elution amount of metal ions” was developed, as disclosed in Patent Document 3. Thus, the hot workability was improved and the corrosion resistance of a welded portion was also improved, resulting in increased convenience, so that it is possible to cope with complicated shapes.
Furthermore, Patent Document 4, “Ni-based alloy anti-corrosion plate having superior high temperature corrosion resistance”, discloses that high-Cr-containing Ni-based alloy exhibits superior hot temperature corrosion resistance in a C heavy oil-fired boiler environment.
Furthermore, “Ni-based alloy having superior corrosion resistance to hydrogen sulfide and hydrogen selenide” disclosed in Patent Document 5 is also useful in applications for a high temperature corrosion environment other than for waste gas of a boiler.
As corrosion resistant applications, alloys are used as those for forming a member for use in a reaction vessel for handling therein acids, such as pharmaceutical intermediates, or those for forming a member for use in a heat exchanger for handling therein nitric hydrofluoric acid.
Suitable applications of “corrosion-resistant Ni—Cr-based alloy having superior bend formability” disclosed in Patent Document 1 and “Ni-based alloy having superior high temperature workability and having superior corrosion resistance with a significantly small elution amount of metal ions” disclosed in Patent Document 3 include a member for handling therein nitric hydrofluoric acid, making use of an advantageous characteristic of corrosion resistance in a wet environment, and a reaction vessel member for use in a chemical plant, for example.
Patent Document 6 discloses “Ni—Cr-based alloy having superior resistance to corrosion by nitric hydrofluoric acid”, and reports that a high-Cr-containing Ni-based alloy is an excellent alloy for forming a member for use in a heat exchanger handling therein nitric hydrofluoric acid.
For another example, the high-Cr-containing Ni-based alloy is also used in a member that requires high abrasion resistance, such as a “die member for resin molding” disclosed in Patent Document 7.